inhabiting extreme environments has made more plausible the search for life in stress
environments. Most microorganisms must accommodate a variety of changing
conditions and stresses in their environment in order to survive and multiply
(Selvakumar et al. 2009). This is due to the fact that most life processes are
temperature dependent and life almost comes to a standstill under sub-optimal
temperatures. Cold temperatures affect the cell interiors and a myriad of cellular
processes, rendering microbial cells inactive or often irreversibly damaged. Since
more than 80% of the earth’s biosphere is exposed to temperatures below 5
C,
throughout the year (Hebraud and Potier 1999), microorganisms capable of coping
with low temperature stress have naturally evolved in several environments. Considering their ubiquity and dominance, cold adapted microorganisms are widely
regarded as the most successful colonizers of our planet (Russell 1990).
To survive at cold temperature microorganisms require to exhibit at least a few of
a range of adaptive behaviors and physiological adjustments. Studies on
psychrophiles have revealed that these such adaptations include lipid modification
to maintain membrane fluidity, accumulation of polyols, genome adaptations, and
production of cold shock proteins (Csps) and cold-active enzymes, oxidative
enzymes, including enzymes important for protein synthesis (Berger et al. 1996;
Ray et al. 1994a, b, c, d, e; Chattopadhyay et al. 2011). To survive under freezing
conditions, some bacteria have developed a variety of strategies, such as the maintenance of membrane fluidity and constant metabolic activities (Kawahara et al. 2001).
Also, it has been suggested that trehalose, glycerol, and sorbitol are major
cryoprotectants for prokaryotic cells to response to freezing temperature, thereby
maintaining some enzyme activities in vivo (Kawahara et al. 2001). However, it is
known that cryotolerance in some bacterial species is associated with fatty acid
changes in membrane lipids (DeAngelis and Gobbetti 2004), as well as certain
culture conditions (Zhao and Zhang 2005). Although some polar bacteria possess
antifreeze proteins (AFPs) when they are living at the junction of ice crystals
(Deming 2002), the accumulation of molecules that inhibit ice recrystallization
(IR) could be part of an adaptive response in Arctic and Antarctic microbes (Muryoi
et al. 2004; Xu et al. 1998). In contrast, some microorganisms have ice-nucleating
protein complexes that promote the growth of ice growth around the cell surface to
avoid lethal intracellular freezing. On the other hand, some bacteria possess antifreeze protein or anti-ice nucleating proteins that are believed to contribute to freeze
tolerance of organism (Panicker et al. 2002).
In this context, life in the cold environments has a lot of significance, and
adaptations of microorganisms to these extreme cold temperature’s conditions are
of major interest. Since the cold adaptation requires a complex range of structural
and functional adaptations, and these adaptations render cold-adapted organisms
very useful for a number of biotechnological applications. The present review
describes adaptive strategies and the resulting biotechnological perspectives of
bacteria inhabiting low-temperature environments.
6 Plant Growth Promoting Rhizobacteria: Mechanisms and Alleviation of Cold Stress. . . 187
environments. Most microorganisms must accommodate a variety of changing
conditions and stresses in their environment in order to survive and multiply
(Selvakumar et al. 2009). This is due to the fact that most life processes are
temperature dependent and life almost comes to a standstill under sub-optimal
temperatures. Cold temperatures affect the cell interiors and a myriad of cellular
processes, rendering microbial cells inactive or often irreversibly damaged. Since
more than 80% of the earth’s biosphere is exposed to temperatures below 5
C,
throughout the year (Hebraud and Potier 1999), microorganisms capable of coping
with low temperature stress have naturally evolved in several environments. Considering their ubiquity and dominance, cold adapted microorganisms are widely
regarded as the most successful colonizers of our planet (Russell 1990).
To survive at cold temperature microorganisms require to exhibit at least a few of
a range of adaptive behaviors and physiological adjustments. Studies on
psychrophiles have revealed that these such adaptations include lipid modification
to maintain membrane fluidity, accumulation of polyols, genome adaptations, and
production of cold shock proteins (Csps) and cold-active enzymes, oxidative
enzymes, including enzymes important for protein synthesis (Berger et al. 1996;
Ray et al. 1994a, b, c, d, e; Chattopadhyay et al. 2011). To survive under freezing
conditions, some bacteria have developed a variety of strategies, such as the maintenance of membrane fluidity and constant metabolic activities (Kawahara et al. 2001).
Also, it has been suggested that trehalose, glycerol, and sorbitol are major
cryoprotectants for prokaryotic cells to response to freezing temperature, thereby
maintaining some enzyme activities in vivo (Kawahara et al. 2001). However, it is
known that cryotolerance in some bacterial species is associated with fatty acid
changes in membrane lipids (DeAngelis and Gobbetti 2004), as well as certain
culture conditions (Zhao and Zhang 2005). Although some polar bacteria possess
antifreeze proteins (AFPs) when they are living at the junction of ice crystals
(Deming 2002), the accumulation of molecules that inhibit ice recrystallization
(IR) could be part of an adaptive response in Arctic and Antarctic microbes (Muryoi
et al. 2004; Xu et al. 1998). In contrast, some microorganisms have ice-nucleating
protein complexes that promote the growth of ice growth around the cell surface to
avoid lethal intracellular freezing. On the other hand, some bacteria possess antifreeze protein or anti-ice nucleating proteins that are believed to contribute to freeze
tolerance of organism (Panicker et al. 2002).
In this context, life in the cold environments has a lot of significance, and
adaptations of microorganisms to these extreme cold temperature’s conditions are
of major interest. Since the cold adaptation requires a complex range of structural
and functional adaptations, and these adaptations render cold-adapted organisms
very useful for a number of biotechnological applications. The present review
describes adaptive strategies and the resulting biotechnological perspectives of
bacteria inhabiting low-temperature environments.
6 Plant Growth Promoting Rhizobacteria: Mechanisms and Alleviation of Cold Stress. . . 187